The present invention relates to novel cyano substituted diphenoquinones which are useful as oxidizing agents and electron acceptors in charge-transfer complex formation and to a process for preparing them.
Charge-transfer complexes are well-known to be utilized as electron materials in the electrophotography and electrostatic record fields. As the representative complex, there is known one composed of the electron acceptor tetracyanoquinodimethane (TCNQ) and the electron-donor tetrathiafulvalene (TTF). The phenomenon of high electrical conductivity of 1.47.times.10.sup.-4 .OMEGA..sup.-1 cm.sup.-1 at 66.degree. K. in this complex was reported by D. O. Cowan et al in 1973 (J. Am. Chem. Soc., 95, 948-949 (1973) and has aroused intense interest.
It is also known that the electrical conductivity of the charge-transfer complex is greatly dependent on the electron-acceptor, especially it is closely related to the molecular structure (flatness and symmetry), electron-transfer power (redox potential) and large transfer integral (size of molecule) of the electron acceptor.
We have engaged in studies on the syntheses and electronic structures of diphenoquinones substituted by electron-withdrawing groups and previously reported that 2,2',6,6'-tetrachloro or tetrabromodiphenoquinone and 2,6'-dicyano-2',6-dibromodiphenoquinone are useful as electron acceptors because of their higher redox potentials in comparison with the generally employed electron acceptors such as chloranil and TCNQ (see, Abstracts 10th Synposium on Structural Organic Chemistry, pages 164-167 (1977)).